Never. As an old time tubular rider, I consider it bad luck to remove any tire that's OK. That philosophy carries onto my commuter and other bikes even though they don't have tubulars. It dovetails perfectly with my basic laziness and rule never to do unnecessary work on my bikes.
__________________
FB
Chain-L site
An ounce of diagnosis is worth a pound of cure.
Just because I'm tired of arguing, doesn't mean you're right.
“One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN
WARNING, I'm from New York. Thin skinned people should maintain safe distance.